ZippyDDoodah
Structural
- Jun 7, 2009
- 38
Hi, I have two general questions regarding response spectrum analysis (RSA), questions which would also apply to any frequency domain loading such as harmonic loads from pressure pulsations or unbalanced vibrating equipment
1) Since results of RSA and other frequency domain loading are positive values only, how is this "limitation" of RSA results typically accounted for in piping design code compliance and for calculation of equipment loads? The sign of the RSA results could make a difference when combining with other loads
2) Is the pipe/structure interaction typically ignored in pipe stress analysis and design? In a seismic event in particular, it would seem that the coupled effect of piping (and equipment) with the structure could have a significant impact on results. The sway of a structure loaded with equipment and piping during an earthquake could whip the piping around in unexpected ways that could potentially damage equipment connected to piping and/or overstress the piping. Of course, the structural eng. should give notice to piping on large deflections from lateral loads
In structural analysis and design, we typically model pipes, equipment, cable trays, etc. as loads, and we include these loads as part of our mass model when there is dynamic analysis. This is not a perfect solution for dynamic analysis, since gaps and friction are ignored, many of the loads are approximated with 'fudge factors' for safety margin, and equipment loads that are offset from the supporting frames are often assumed to be acting on the centerline of the frame.. but still, even that approach seems to be miles ahead of the simplified "rigid support" assumptions that I see being commonly made in pipe stress analysis.. although I don't see any other practical alternative short of spending a ton of time creating a nonlinear structural model with everything
1) Since results of RSA and other frequency domain loading are positive values only, how is this "limitation" of RSA results typically accounted for in piping design code compliance and for calculation of equipment loads? The sign of the RSA results could make a difference when combining with other loads
2) Is the pipe/structure interaction typically ignored in pipe stress analysis and design? In a seismic event in particular, it would seem that the coupled effect of piping (and equipment) with the structure could have a significant impact on results. The sway of a structure loaded with equipment and piping during an earthquake could whip the piping around in unexpected ways that could potentially damage equipment connected to piping and/or overstress the piping. Of course, the structural eng. should give notice to piping on large deflections from lateral loads
In structural analysis and design, we typically model pipes, equipment, cable trays, etc. as loads, and we include these loads as part of our mass model when there is dynamic analysis. This is not a perfect solution for dynamic analysis, since gaps and friction are ignored, many of the loads are approximated with 'fudge factors' for safety margin, and equipment loads that are offset from the supporting frames are often assumed to be acting on the centerline of the frame.. but still, even that approach seems to be miles ahead of the simplified "rigid support" assumptions that I see being commonly made in pipe stress analysis.. although I don't see any other practical alternative short of spending a ton of time creating a nonlinear structural model with everything
